In conventional high-pressure fuel systems, an engine-driven fuel pump is a key source of unwanted audible noise as well as a source of fuel pressure pulsations, which complicate the fuel metering task. Management of these pulsations requires 1) extra volume in the fuel rail, which increases the time required to achieve target fuel pressure at engine start, 2) orifices, which increase the pump power consumption, and 3) an increased relief valve set-point, which increases the pressure at which the injectors must open and thus compromises the configuration of the injectors for other targets.
The present state-of-the-art high-pressure fuel pump includes a solenoid and an inlet check valve. To control the volume of fuel pumped, the solenoid holds the electrically-operated inlet check valve open during the beginning of the pumping stroke, then allows the inlet check valve to close at a time during the pumping phase calculated to cause precisely the desired quantity of fuel to be pumped into the fuel rail. This occurs at any fuel demand less than 100% of the pump capability, which is the case nearly 100% of the time during engine operation. Given the practical requirement for an approximately sinusoidal movement of the pump piston, the piston velocity, and therefore the velocity of fuel flowing backward through the inlet check valve before it is allowed to close, is at a maximum just before the valve closes. This high velocity results in slamming of the inlet check valve, a key source of audible noise, and further results in a significant pump-internal fuel pressure spike of hundreds of psi due to reversal of the fuel motion. These fuel pressure spikes result in adverse design requirements for the opening pressure of a required pressure relief valve, the volume of the fuel rail, and the opening pressure of the fuel injectors.
The rapid movement of the solenoid armature between its end stops, one cycle per pumping stroke, is also a significant source of audible noise.
Thus, there is a need to provide control structure for an engine-driven fuel pump that that reduces the audible noise and pressure pulsations, enabling a design choice of reducing the fuel rail volume, enlarging the orifices, and/or reducing the relief valve set-point.